1. Field of the Invention
The present invention relates to a projection type display apparatus and, more particularly, to a projection type display apparatus for displaying a full-color image on a display surface such as a screen using a mirror array device as optical modulation means.
2. Related Background Art
Along with the advent of the age of multimedia, image display apparatuses are used in every scene. Generally, display apparatuses for forming an image by modulating light are roughly classified into two types. One type is a direct viewing image type display apparatus such as a direct viewing CRT (Cathode Ray Tube) and direct viewing LCD, and the other type is a projection type display apparatus, including an LCD (Liquid Crystal Display), and a reflecting mirror device such as DMD (Deformable Mirror Device), or AMA (Actuated Mirror Array).
Since projection type display apparatuses can easily increase the screen size, front projectors for presentation or the like and rear projectors for a home theater or the like are becoming widely used. In such a projection type display apparatus using a liquid crystal panel or reflecting mirror device, the liquid crystal panel or reflecting mirror device serving as an optical modulation device is illuminated with light from a light source, and transmitted or reflected light is made incident on a screen or the like through a projecting optical system, thereby forming an image.
Although a direct viewing CRT is excellent in image quality, the weight and volume of the apparatus increase, and the manufacturing cost increases as the screen size increases. To the contrary, a projecting liquid crystal display apparatus can be made relatively thin, and the weight and volume can be reduced because its optical structure is simple. However, since an LCD normally uses linearly polarized light, the light utilization efficiency is as low as 1% to 5%. In addition, liquid crystal molecules respond slowly, and the liquid crystal layer is readily heated.
To solve the above problems, projection type display apparatuses using a reflecting mirror device such as a DMD or AMA have been developed. Currently, such projection type display apparatuses can obtain a light utilization efficiency of 5% to 10%. In addition, optical modulation is not affected by the polarization state of incident light and does not affect the polarization state of reflected light.
AMAs serving as reflecting mirror devices are roughly classified into a bulk type and a thin-film type. A bulk AMA is disclosed in U.S. Pat. No. 5,469,302 by Dae-Young Lim. To obtain the bulk AMA, a ceramic layer having a multilayered structure is cut into a thin ceramic wafer with a metal electrode formed inside, the ceramic wafer is mounted on an active matrix incorporating a transistor, the resultant structure is fabricated by sawing, and a mirror is formed on it.
As shown in FIG. 3, a thin-film AMA is disclosed in U.S. Pat. No. 5,815,305. Referring to FIG. 3, the thin-film AMA has an active matrix 31, an actuator 33 formed on the active matrix 31, and a mirror 35 formed on the actuator 33.
The active matrix 31 has a substrate 37, and Mxc3x97N (M and N are positive integers) transistors (not shown) formed on the substrate 37, and Mxc3x97N connection terminals 39 formed on the respective transistors.
The actuator 33 has a support portion 41 formed on the active matrix 31 and having the connection terminal 39, a first electrode 43 whose lower end on one side is attached to the support portion 41 and other side is formed in parallel to the active matrix 31, an interconnection or conductive tube 49 formed in the support portion 41 to connect the connection terminal 39 and first electrode 43, a deformable layer 45 formed on the first electrode 43, a second electrode 47 formed on the deformable layer 45, a spacing member 51 formed on one side of the second electrode 47, and a support layer 53 whose lower end on one side is attached to the spacing member 51 and other side is formed in parallel to the second electrode 47. The second electrode 47 is connected to the active matrix 31 by an interconnection (not shown). The mirror 35 is formed on the support layer 53.
When a predetermined electrical signal (voltage) corresponding to an image signal is applied to the first electrode 43 of each pixel through the active matrix 31, each pixel actuator 33 tilts by a predetermined angle, and accordingly, each pixel mirror 35 tilts.
Such a thin-film AMA is manufactured using semiconductor manufacturing processes. For this reason, the mirror array has a perfect quality so that light enough to display digital image with a high-luminance and high-contrast under normal indoor illumination conditions can be transmitted to the screen. In other words, a thin-film AMA is a reflection-type optical modulator using a thin-film piezoelectric actuator in relation to a microscopic mirror and has been developed to obtain a tilt angle enough to provide high contrast and a light utilization efficiency enough to provide high luminance. A thin-film AMA has also been developed to ensure uniformity in a large scale integration across 300,000 pixels of mirrors formed from a single pattern.
As for forming a projection type display apparatus using a reflecting mirror device such as a thin-film AMA or DMD, a typical arrangement is disclosed in, e.g., Japanese Patent Application Laid-open No. 8-21977. That is, white illumination light is time-divisionally color-separated by a rotary color filter, a reflecting mirror device is illuminated with each color light component, and reflected light is guided into or outside the aperture of a projecting lens in accordance with tilt drive of each pixel mirror, thereby obtaining a predetermined full-color projected image.
In the prior art disclosed in Japanese Patent Application Laid-open No. 8-21977 described above, however, in projecting a full-color image, the illumination system has at least a rotary filter, a rotary filter drive motor, and a rotary synchronized signal processing system for color separation, resulting in complex structure. Additionally, since the rotary filter, i.e., a section rotatably driven at a high speed of up to 10,000 rpm is present, the system has problem in vibration noise and reliability.
One aspect of the present invention is to provide a projection type display apparatus comprising:
a mirror array device having a plurality of tiltable pixel mirrors each having a diffraction grating on a surface to perform optical modulation by the plurality of pixel mirrors;
an illumination optical system for illuminating the mirror array device; and
a projecting optical system for projecting reflected light from the mirror array device onto a projected surface.
An apparatus described above preferably has a feature that each pixel mirror is not tilted to display black on the projected surface.
An apparatus described above preferably has a feature that the tilt angle of each pixel mirror is maximized to display black on the projected surface.
An apparatus described above preferably has a feature that each pixel mirror is tilted by a predetermined angle to do display black on the projected surface.
An apparatus described above preferably has a feature that the projecting optical system has an aperture which shields, of the reflected light components from the mirror array device, a light component which is not to be projected onto the projected surface.
An apparatus described above preferably has a feature that a color to be displayed on the projected surface is switched by changing a tilt angle of each pixel mirror.
An apparatus described above preferably has a feature that a color to be displayed on the projected surface is switched between red, green, and blue by changing the tilt angle of each pixel mirror.
An apparatus described above preferably has a feature that
tilt angles of the pixel mirrors have a plurality of angle ranges that do not overlap, and
a color of light to be projected onto the projected surface is switched by switching the angle range of the tilt angle.
An apparatus described above preferably has a feature that
tilt angles of the pixel mirrors have first, second, third, and fourth angle ranges that do not overlap,
when the tilt angle falls within the first range, red is displayed on the projected surface,
when the tilt angle falls within the second range, green is displayed on the projected surface,
when the tilt angle falls within the third range, blue is displayed on the projected surface, and
when the tilt angle falls within the fourth range, black is displayed on the projected surface.
An apparatus described above preferably has a feature that gray level display of each color is performed by changing the tilt angle of each pixel mirror within the first, second, and third angle ranges.
An apparatus described above preferably has a feature that gray level display of each color is performed by changing the tilt angle of each pixel mirror.
An apparatus described above preferably has a feature that color display of one pixel is performed by mixing the color light components from the pixel mirrors by time color mixing.
An apparatus described above preferably has a feature that color display of one pixel is performed by mixing the color light components from the plurality of pixel mirrors adjacent to each other.
An apparatus described above preferably has a feature that the diffraction grating is an echelon grating.
An apparatus described above preferably has a feature that in a section perpendicular to a rotational axis in tilting the pixel mirror, the diffraction grating has a staircase shape.
An apparatus described above preferably has a feature that a direction in which light diffracted by the pixel mirror is distributed and a tilt direction of the pixel mirror are in the same plane.
An apparatus described above preferably has a feature that each diffracted light of each color is deflected in a separation direction of each color light component diffracted by the pixel mirror by tilting the pixel mirror.
The other aspect of the present invention is to provide a mirror array device comprising a plurality of tiltable pixel mirrors each having a diffraction grating on a surface,
wherein optical modulation is executed by the plurality of pixel mirrors.
A device described above preferably has a feature that the diffraction grating is an echelon grating.
A device described above preferably has a feature that a direction in which light diffracted by the pixel mirror is distributed and a tilt direction of the pixel mirror are in the same plane.
A device described above preferably has a feature that each diffracted light of each color is deflected in a separation direction of each color light component diffracted by the pixel mirror by tilting the pixel mirror.